(1) Field of the Invention
The present invention relates to an electrochemical system, in particular a magnesium solution phase catholyte seawater electrochemical system, and to a process for generating electrical power using said system.
(2) Description of the Prior Art
Magnesium-seawater batteries have been developed, all of which include solid cathodes, including silver chloride, cuprous chloride, lead chloride, cuprous iodide, cuprous thiocyanate and manganese dioxide. Further, primary batteries employing aqueous electrolytes have been developed by various governmental and commercial laboratories in the U.S. and elsewhere since the 1940s. Emphasis has been placed on aluminum and magnesium anodes due to their high faradic capacity, low atomic weight, and high standard potentials. Of particular interest is their application to undersea vehicles as a result of the availability of seawater to act as an electrolyte or electrolyte solution, thus further enhancing their effectiveness as an energy source on a systems basis.
Magnesium/cuprous chloride and magnesium silver chloride were used as cathode materials in prior art battery systems. Eventually they were replaced with lower cost alternative cathodes such as lead chloride and manganese dioxide; but with equally lower specific energy. The development of higher specific energy systems included replacing magnesium with aluminum while retaining the silver oxide cathode. This enabled exceptional specific power and energy but with increased cost. To reduce the cost without compromising specific energy, the expensive silver oxide cathode was replaced with solution phase catholytes, such as hydrogen peroxide or sodium hypochlorite. These advancements are extremely promising by virtue of the reduced cost of materials while achieving specific energies upwards of 100 Wh/lb at current densities of 100-1200 mA/cm.sup.2.
Other countries, notably Sweden and Norway, have successfully employed magnesium-seawater batteries whereby oxygen saturated in the seawater electrolyte is reduced on a catalytic cathode surface opposite the magnesium anode. This is highly efficient on a systems basis due to the fact that there is no sodium hydroxide required, greatly reducing the system weight. However, limited oxygen availability limits specific energies to under 100 Wh/lb.
Various types of batteries are shown in the patent literature. For example, U.S. Pat. No. 4,063,006 to Murphy illustrates an aqueous electrolyte battery in which liquid oxychlorides are fed to a cathode chamber. The oxychlorides flow through a porous carbon electrode. At the electrode, the oxychlorides are reduced and the reaction products dissolve in an aqueous electrolyte flowing by the face of the carbon electrode opposite to that in which the oxychlorides are introduced. Metal standoffs connect to the porous electrode for use as conductors while maintaining spacing in the cathode chamber.
U.S. Pat. No. 4,822,698 to Jackovitz et al. relates to a battery having an anode selected from the group consisting of magnesium, zinc, and mixtures and alloys thereof, an oxygen electrode as the cathode, and means for maintaining the anode and the cathode in an electricity generating relationship when the battery is placed in salt water. The '698 patent also describes a method of producing electricity by positioning the anode and cathode in a saline electrolyte.
U.S. Pat. No. 4,910,102 to Rao et al. relates to a battery assembly and a process for operating same. The battery assembly is comprised of bipolar electrodes disposed between an inert cathode current collector acting as a hydrogen electrode and an anode plate formed from material selected from the group consisting of aluminum, magnesium, aluminum alloys, magnesium alloys and mixtures thereof. The battery is configured for electrolyte flow wherein the electrolyte includes hydrogen peroxide in an amount sufficient to provide 0.5 to about 30 volume percent solution.
U.S. Pat. No. 4,910,104 to Rao et al. relates to a deferred actuated battery assembly comprised of a plurality of bipolar electrodes disposed between an inert cathode current collector acting as a hydrogen electrode and an anode plate formed from a material selected from the group consisting of aluminum, magnesium, aluminum alloys, magnesium alloys, and mixtures thereof and configured for electrolyte flow therebetween.
U.S. Pat. No. 5,314,766 to Witherspoon et al. relates to a lead acid battery electrode and a method of manufacturing same. The positive plates are prepared by forming partially oxidized tetrabasic lead sulfate having at least a part of the oxide portion in the form of alpha lead dioxide and forming beta lead dioxide. Next the oxidized tetrabasic lead sulfate and the beta lead dioxide are intermingled in a wet mixture. The wet mixture is applied to the oxidized surface of a lead support substrate. Then, it is heated and pressed for a time and at a temperature and compressive load sufficient to form an adhered or retained coating of active material on the substrate. The oxidized tetrabasic lead sulfate is formed by reaction of tetrabasic lead sulfate with magnesium hydroxide and sodium persulfate. Preferably, beta lead dioxide is formed by reacting red lead oxide with nitric acid to provide an oxidation product, at least a major portion of which is beta lead oxide, and which has a surface area of at least 10 m.sup.2 /gram.
U.S. Pat. No. 5,445,905 to Marsh relates to a dual flow battery comprising an aqueous hydrogen peroxide catholyte, an aqueous anolyte, a porous solid electrocatalyst capable of reducing the hydrogen peroxide and separating said anolyte, and an aluminum anode positioned within said anolyte. Separation of catholyte and anolyte chambers prevents hydrogen peroxide poisoning of the aluminum anode.
Many of these prior art batteries are expensive to manufacture and inordinately large. Further, many of these prior art batteries are unreliable.